1. Field of the Invention
The present invention relates to the field of interferometry. In particular the present invention relates to non-periodic, wavefront-dividing interferometers that increase efficiency.
2. Description of the Related Technology
A schematic of a Michelson Fourier Transform (FT) interferometer 10 is shown in FIG. 1. Michelson FT spectrometers are amplitude-dividing interferometers using dielectric beamsplitters. In FIG. 1 the incident light enters the interferometer and contacts the beamsplitter 12 and two mirrors 11 that transmit the light to a detector 18. The detector 18 is operatively connected to amplifier 4 and a computer 5 that can calculate the Fourier transform. An ideal beamsplitter for use in a Michelson FT interferometer transmits 50% of the light and reflects 50% of the incident light beam. This maximum-efficiency situation gives the highest signal-to-noise ratio in the detected signal while using a minimum measurement time. While the usage of the Michelson FT interferometer with dielectric beamsplitters is effective for limited spectral regions, since its introduction in the 1950s attempts to design a beamsplitter that operates over a large spectral region have been unsuccessful.
Due to the lack of beamsplitters that are able to accommodate a large range of wavelengths, when measuring a range of wavelengths the beamsplitter has to be replaced when wavelengths not accommodated by the installed beamsplitter are required. The process of replacing beamsplitters is inconvenient and time consuming because the beamsplitters must be aligned with a high degree of accuracy in a Michelson FT interferometer. For example, the commercial Bruker Fourier transform infrared spectrometer uses five different beamsplitters in order to cover the THz through infrared spectral region. The changing of beamsplitters is inconvenient in general and especially so for flight instruments and portable ground-based instruments.
In addition to the Michelson FT interferometer, another type of interferometer is the wavefront dividing interferometer 15 shown in FIG. 2. In the wavefront dividing interferometer 15 the incident light strikes two sets of reflectors 14 and 16. The reflectors are displaced with respect to one another to produce an interferogram. The light is then reflected back to a detector 18. When using a wavefront dividing interferometer 15 there is no need to use beamsplitters. This has obvious advantages in reducing the number of components used in the interferometer, however the efficiency of the light transmission may not be ideal.
Therefore, there is a need in the field for an interferometer that enables usage over a large range of wavelengths and obviates the need for replacement or adjustment to the interferometer.